It is known in the art that the power of electrically excited, molecular discharge lasers, especially the CO.sub.2 lasers, can be significantly improved if such lasers can be operated at atmospheric pressures and above. What is sought are means to provide more efficient excitation of the gas volume, i.e., more efficient and effective electrical pumping, greater energy density, uniform optical quality, and greater collisional line broadening. The problem presently is one of achieving uniform electrical discharges in the gas volume at high pressures, that is, atmospheric pressures and above. Mode-locked CO.sub.2 gas lasers operating at pressures above one atmosphere and capable of producing laser pulses with energies in the 10.sup.4 to 10.sup.6 J range and having a time duration ranging from 10.sup.-11 to 10.sup.-9 second are useful in fusion initiation studies.
The art shows that attempts to achieve high current uniform discharges in laser gases at pressures of one atmosphere are most commonly directed toward mechanical subdivision of the discharge electrodes, with separate current sources for each subdivision. Thus, for example, laser pumping of He:N.sub.2 :CO.sub.2 mixtures has been achieved at atmospheric pressure using transverse electrical discharges. The technique is characterized by fast (.about.1-2 .mu.sec) discharges between overvolted electrode structures which deposit electrical energy into the laser gas mixture in a time short compared with the arc formation time, although the latter stages of even these discharges may show formation of constricted arcs. The distribution of the electrical energy over a volume is accomplished by the use of multielectrode arrays in which each electrode has its own capacitor feed or has a ballast resistor to limit the current. More recently reported devices use dielectric-coated electrodes an double discharge circuits to produce a more or less uniform electron-ion plasma sheath to initiate the discharge.
These techniques seek to avoid or minimize the problems of high-current constricted arcs in self-sustained discharges through the use of fast discharges which deposit the energy into the gas before arcs or channeling can form. The instability mechanisms which lead to arc formation in self-sustained discharges are not well understood, but have been attributed to cathode processes involving field emission, local heating, and other spark charge distribution of the cathode electric field.
Arcing or channeling severely restricts the amount of energy that can effectively and efficiently be transferred to the laser gas through electrical pumping. It is highly desirable therefore to stabilize a plasma throughout substantially the entire volume of the laser gas for a time sufficient for efficient pumping to occur.